1. Field of the Invention
The present invention relates to a polymeric contact lens material of improved oxygen permeability. More particularly, the present invention relates to a fluoroalkyl-containing monomer and a polymeric composition containing the monomer, which is useful as a contact lens material.
2. Description of the Prior Art
It is known that contact lenses may be made of polymethylmethacrylate (PMMA). This material is not harmful to the human body and shows good optical permeability. However, the contact lenses made of the PMMA may interfere the metabolism of the eyes when worn for a long time because of the properties of the material such as high stiffness and low oxygen permeability.
In order to solve these problems, intensive researches have been made. For example, a method has been suggested which comprises copolymerizing a siloxanyl alkyl ester of methacrylic acid with an acrylic monomer to obtain a polymer having enhanced oxygen permeability. Such improved oxygen permeability is considered to be attributed to the high oxygen-solubility of the siloxane group contained in the resulting polymer. The representative examples of this method are described in U.S. Pat. Nos. 4,330,383; 4,491,905; 4,424,328; 4,463,149; 4,535,138; 4,826,936; 4,826,889; 4,769,431; 4,625,007; 4,604,479; 4,582,884; and 4,535,138.
Other methods have been proposed in U.S. Pat. Nos. 4,996,275; 4,686,267; and 4,661,573, which comprises copolymerizing a silicone-containing monomer with an acrylic monomer. In accordance with this method, oxygen permeability can be increased by increasing the amount of the silicone-containing monomer to be copolymerized. In this method, an increased amount of the silicone-containing monomer may result in the degradation of ocular biocompatibility because the monomer reduces the processing ability of the resulting polymer and renders the polymer highly hydrophobic.
U.S. Pat. No. 4,990,582 proposes a method of preparing a contact lens material of improved oxygen permeability, wherein a fluorine-containing monomer is used. This type of the monomer is capable of providing the oxygen permeability, the silicone-containing monomer, without decreasing the processing ability significantly. However, this method suffers from the degraded the ocular biocompatibility of the resulting polymer. In other words, the larger the content of fluorine is, the higher the hydrophobicity is, even though the oxygen permeability is improved. Since the most of the fluorine-containing monomers are made by esterifying acrylic acid, methacrylic acid or itaconic acid with a fluoroalkyl alcohol, they have only one ester group per fluoroalkyl as a hydrophilic group. This is the reason why such fluorine-containing monomers have a lower concentration of the hydrophilic group.
An attempt has been made to improve biocompatibility of the homopolymers of either silicone-containing monomers or fluorine-containing monomers, or the copolymer thereof. For example, U.S. Pat. No. 3,619,044 suggests to introduce a number of hydrophilic groups into the surface of the contact lenses. However, this method suffers from the defects that the transparency of the lenses decreases significantly with the lapse of their wearing time, because the proteins contained in tears are deposited on the surface of the lenses.